Generally, a vehicle is provided with a passenger protecting system for protecting passengers in a collision of the vehicle. The passenger protecting system has, for example, an airbag device for deploying an airbag to protect the head portion or the like of the passenger, and/or a pre-tensioner device for taking up a slack of a seat belt of the vehicle.
The airbag device and the pre-tensioner device are controlled by a control unit such as an ECU. The ECU performs a determination of a vehicle collision based on signals from sensors mounted to the vehicle, and actuates the airbag device and the pre-tensioner device when the vehicle collision is determined.
For example, the sensor for detecting the vehicle collision can be constructed of an acceleration sensor for detecting an acceleration variation of the vehicle, a touch sensor which is attached to a periphery portion of the vehicle to detect a stress thereat, a pressure sensor for detecting a pressure variation in a space formed at the periphery portion of the vehicle, or the like.
It is desirable for the passenger protecting system to protect the passenger not only from a vehicle collision in the vehicle traveling direction (i.e., vehicle front-rear direction), but also from a side collision of the vehicle which causes a vehicle-width-direction impact on the vehicle.
For example, as disclosed in JP-2-249740A, the airbag device for protecting the passenger from the side collision of the vehicle is provided with a side airbag, which can be deployed according to detection signals of the pressure sensor. The pressure sensor detects the variation of an inner pressure of the vehicle door.
However, in this case, because the pressure sensor is mounted to the vehicle door to detect the inner pressure thereof, the vibration information of the vehicle which is excited by the impact load of the collision will be included in the detection signals of the pressure sensor. Specifically, when the vehicle collision occurs, the impact load due to the collision is transmitted to the vehicle body such as the vehicle door. As a result, the vehicle door is excited to vibrate, and the vibration will be transferred to the pressure sensor. According to the conventional side-airbag system, the vibration of the vehicle door is added to the inner pressure thereof to be detected by the pressure sensor, thus causing an error in the collision determination which is performed based on the detection signals of the pressure sensor.
Although the error can be reduced by a correction of the detection signals of the pressure sensor by the ECU, the responsivity is inferior and processing time is needed, which is undesirable.